1. Field of the Invention
The present invention relates to an optical disc apparatus for recording data on an optical disc.
2. Description of the Related Art
Recently, various types of optical disc apparatuses for recording or reproducing data using a light beam have been developed. As write once type optical discs, CD-R/RW discs, DVD-RAM discs, DVD-R/RW discs have been, for example, developed.
A DVD-R/RW has a convexed pit referred to as a “pre-pit” in each of land tracks interposing groove tracks (land pre-pit). A land pre-pit is detected by level-slicing a push-pull signal at a prescribed slicing level. The push-pull signal is obtained when the groove track is irradiated with a light beam.
In order to obtain a recording clock signal in synchronization with a linear velocity of the rotating optical disc which is rotating, the track is waved at a prescribed cycle. This wave is referred to as a “wobble”. Wobbles are located so as to have a prescribed phase relationship with the land pre-pits. Like the land pre-pit, the wobble is also detected by level-slicing a push-pull signal at a prescribed slicing level. By detecting the frequency of the wobbles and multiplying the frequency by a prescribed value, a recording clock signal corresponding to a unit time length of a recording mark can be obtained.
In general, data is recorded on a DVD-R/RW disc in synchronization with a recording clock signal obtained from the wobbles based on the land pre-pit signal. In the case where data is already recorded on the DVD-R/RW disc, very highly precise recording position control is required so that there is no gap or discontinuity between the previously recorded data and the newly recorded data.
The DVD-R/RW disc has a track pitch of 0.74 μm, which is half of the track pitch of a CD-R/RW disc of 1.6 μm. The CD-R/RW disc is another write once type optical disc. Due to such a narrow track pitch, in the DVD-R/RW disc, the influence of interference from tracks adjacent to the track of interest (i.e., crosstalk) is highly noticeable. A fluctuation in the wobble amplitude and phase caused by the crosstalk affects, in the form of jitters, the recording clock obtained by multiplying the frequency of the wobbles by a prescribed value. The recording clock extracted from the wobbles is mainly used for generating a recording timing signal for the purpose of, for example, synchronization of recording data. Therefore, the jitters in the recording clock may undesirably deviate the recording position.
A land pre-pit signal itself involves a jitter component due to, for example, interference with the recording mark which is already recorded, and a difference between the power of the light beam in the state of forming a recording mark for the purpose of recording and the light beam in other states.
For these reasons, recording of data which is performed after the recording timing signal is determined based on the land pre-pit signal may result in the previously recorded data and the newly recorded data being undesirably discontinuous. Such discontinuity affects bit synchronization or frame synchronization which is performed for reproduction. As a result, the connection portion between the previously recorded data and the newly recorded data cannot be reproduced in a superb manner.
In order to solve this problem, Japanese Laid-Open Publication No. 2000-187947 titled “Optical disc recording apparatus” proposes an optical disc of a system for reproducing a synchronization signal included in the previously recorded data and adjusting a timing of recording the data to be newly recorded based on the synchronization signal.
Depending on the influence of the crosstalk or the difference between the states of recording, a reproduction clock obtained from the previously recorded data and a reproduction clock obtained from the newly recorded data may have different frequencies or phases.
In such a case, there is a problem in that the connection portion between the previously recorded data and the newly recorded data cannot be reproduced in a superb manner until the frequency of the reproduction clock is stabilized.
In order to solve this problem. Japanese Laid-Open Publication No. 2000-298955 titled “Information recording apparatus and information recording method” proposes an optical disc of a system for synchronizing the frequency or phase of a recording clock to the frequency or phase of the reproduction clock of the previously recorded data and then, after the recording operation starts, recovering the frequency or phase of the recording clock to the original frequency or phase at a prescribed time constant.
However, the optical discs described in the above-described publications have the following problems.
In the system for reproducing a synchronization signal included in the previously recorded data and adjusting the timing of recording the data to be newly recorded based on the synchronization signal, the positional deviation of the previously recorded data remains in the newly recorded data.
The system for synchronizing the frequency or phase of a recording clock to the frequency or phase of the reproduction clock of the previously recorded data and then, after the recording operation starts, recovering the frequency or phase of the recording clock to the original frequency or phase at a prescribed time constant, involves the following problem. Frequency errors of the recording clock, which are generated in a transition state in which the frequency or phase of the recording clock changes after the recording operation starts, are accumulated. Thus, a timing error is generated at a recording position. As a result, a positional deviation occurs for the newly recorded data.
The amounts of deviation of recording position are Accumulated each time data is additionally written and may result in a significant deviation.